1. Field of the Invention
The present invention relates to a hand-held drive-in tool for driving fastening elements in a constructional component or a workpiece and including a drive-in ram displaceably supported in a guide for driving fastening elements in the constructional component or the workpiece, a drive for driving the drive-in ram and having a driving spring member for displacing the drive-in ram, a device for preloading the driving spring member, a locking device having a locking position in which the locking device retains the driving spring member in its preloaded position and including locking means.
2. Description of the Prior Art
In a drive-in tool described above, the driving spring member is formed as a mechanical spring.
The advantage of drive-in tools of the type described above consists in using a low-cost mechanical driving spring member, which permits to economically manufacture this type of drive-in tools. Because a preloading process can last only from ten to several hundred milliseconds, in particular when very strong driving springs are used, it is advantageous when the preloading process is already completely carried out before actuation of the actuation switch of the drive-in tool. It is further necessary that the driving spring is fixed in its preloaded position before actuation of the drive-in process by a locking device, directly or indirectly, e.g., via another element such as the drive-in ram.
A drive-in tool of the type described above is disclosed in U.S. Pat. No. 3,847,322. In the disclosed drive-in tool, a drive-in ram is preloaded against a driving spring member by a motor-driven preloading mechanism. A locking device retains the drive-in ram and the driving spring member in the preloaded position. To this end, the locking device has locking means that lockingly engages a locking surface on the drive-in ram. The locking device is released by an actuation switch, whereby the locking device is lifted off its locking position by a motor-driven mechanism and is displaced in a release position. In the release position of the locking device, the drive-in ram is displaced in the setting direction by the biasing force of the driving spring member for driving a fastening element in a workpiece.
The drawback of the known drive-in tool consists in that the sliding friction between the locking means and the locking surface is relatively high, so that lifting of the locking means off is rather, slow-going. Furthermore, loss of the material due to the sliding friction under a surface pressure is rather high.
Accordingly, an object of the present invention is a drive-in tool in which the above-discussed drawbacks a known drive-in tool is eliminated.